If there are ten or more creature cards total in all graveyards, Avatar of Woe costs less to cast.
Fear (This creature can't be blocked except by artifact creatures and/or black creatures.): Destroy target creature. It can't be regenerated.

Name a nonland card. Target player reveals his or her hand and discards all cards with that name.
Flashback - Sacrifice a creature. (You may cast this card from your graveyard for its flashback cost. Then exile it.)

When Diabolic Servitude enters the battlefield, return target creature card from your graveyard to the battlefield.
When the creature put onto the battlefield with Diabolic Servitude dies, exile it and return Diabolic Servitude to its owner's hand.
When Diabolic Servitude leaves the battlefield, exile the creature put onto the battlefield with Diabolic Servitude.

When Faceless Butcher enters the battlefield, exile target creature other than Faceless Butcher.
When Faceless Butcher leaves the battlefield, return the exiled card to the battlefield under its owner's control.